|Publication number||US7400136 B2|
|Application number||US 10/553,771|
|Publication date||Jul 15, 2008|
|Filing date||Apr 14, 2004|
|Priority date||Apr 22, 2003|
|Also published as||EP1618400A1, US20060267579, WO2004095044A1|
|Publication number||10553771, 553771, PCT/2004/1204, PCT/IB/2004/001204, PCT/IB/2004/01204, PCT/IB/4/001204, PCT/IB/4/01204, PCT/IB2004/001204, PCT/IB2004/01204, PCT/IB2004001204, PCT/IB200401204, PCT/IB4/001204, PCT/IB4/01204, PCT/IB4001204, PCT/IB401204, US 7400136 B2, US 7400136B2, US-B2-7400136, US7400136 B2, US7400136B2|
|Inventors||Jörn Borgert, Volker Rasche|
|Original Assignee||Koninklijke Philips Electronics N.V.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Non-Patent Citations (3), Classifications (14), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates generally to position and/or orientation measurements. In particular, the present invention relates to a tracking method for tracking a sensor in a capture range in a field generated by a field generator, a tracking system for tracking a sensor in a capture range in a field generated by a field generator and to a computer program product comprising computer program code means.
Known systems for performing position measurements use a localization system with a given fixed capture range and accuracy and resolution. Having a fixed size and desirably large capture range often comes at the cost of decreased accuracy in resolution. This bears two problems: either the capture range or the accuracy and resolution do not match the needs of a user.
P. G. Seiler et al: “A novel tracking technique for the continuous precise measurement of tumour positions in conformal radiotherapy” Phys. Med. Biol. 45 (2000) N103-N110 describes a tracking technique using magnetic fields as information carriers between a field generator and a field sensor, similar to other magnetic tracking applications such as Wynn et al “Advanced superconducting gradiometer/magnetometer arrays and a novel signal processing technique” IEEE Trans. Magn. 11 701-7. However, the capture range defined by the field generated with the field generator remains the same for all applications and measurements.
It is an object of the present invention to provide for a localization and tracking of a sensor with a high accuracy and resolution.
According to an exemplary embodiment, this object may be solved with a tracking method for tracking a sensor in a capture range in a field generated by a field generator, wherein a field is generated by means of the field generator for defining the capture range, a region of interest including the sensor is identified within the capture range and the capture range is iteratively narrowed by narrowing the field by means of a field generator to enclose the region of interest.
In other words, the localization and tracking according to this exemplary embodiment of the present invention starts at a coarse level, where the region of interest is identified and navigated to. In the following iterative process, the capture range of the localization and tracking system is narrowed step by step and the accuracy and precision is thus increased. During each step, the region of interest may be subject to measurement of the position with increasing accuracy and precision and a high and steady-going frame rate of acquisition, because the system has to track only one target at a time. The tracking of a plurality of targets often results in a smaller frame rate. Within this application, the term “to narrow” is to be interpreted as including any adjustment with respect to at least one of a size, direction and orientation of the capture range to achieve an adjustment, shifting and/or moving of the capture range. The iteration ends, when the position measurement can be performed at the desired level of accuracy and resolution, either given by the user or the limitations of the system.
According to other exemplary embodiments, a position of at least one coil in the field generator is adjusted, the field generator itself is adjusted or an orientation of at least one coil in the field generator is adjusted for narrowing the capture range. According to these exemplary embodiments, a very simple and effective method for narrowing the capture range is provided, which allows to adjust the capture range with a high degree of accuracy.
Preferably, the method is supported by a “scalable localization system” which can be scaled in terms of the size and position of the box of motion or capture range and the accuracy and resolution.
According to another exemplary embodiment, a tracking system is provided for tracking a sensor in a capture range in a field generated by a field generator, wherein the field generator is adapted to adjust one of a size, direction and orientation of the capture range. Advantageously, the tracking system according to the exemplary embodiment of the present invention allows to meet with an accuracy and resolution required by a user for different applications.
As set forth in the exemplary embodiments, the capture range may be adjusted by adjusting a position of at least one coil in the field generator, by adapting the field generator such that it is moveable and by accordingly moving the field generator or by adjusting an orientation of at least one coil in the field generator. Alternatively, a plurality of coil arrangements may be provided, each generating a different size of field, i.e. capture range, which can be iteratively selected.
According to another exemplary embodiment, a computer program product is provided comprising computer program code means to perform the method according to the present invention when the computer program is executed on a computerized tracking system. Advantageously, the computer program product according to the present invention allows to minimize a computational power required in the tracking system by providing an iterative procedure which can easily be performed.
The capture range is iteratively adjusted to a level where the accuracy and resolution required in a certain application is met. When the capture range is large, the required accuracy and resolution is low. So, the target area can be identified and aimed at. Given this identification, the capture range can be focused and centered around the region of interest, which in turn leads to increased accuracy, resolution and frame rate. This process can be repeated in iterations leading to a small capture range and a large accuracy and resolution.
These and other aspects of the present invention will become apparent from and elucidated with reference to the embodiments described hereinafter.
Exemplary embodiments of the present invention will be described in the following with reference to the following drawings:
In the following exemplary embodiments of the field generator 2, the calculation unit 4 and the sensor 6 will be described in her detail.
The field generator 2 is preferably a magnetic field generator and may comprise six differential coils, which form the edges of the tetrahedron shaped assembly. Each differential coil comprises two coils of opposite polarization, which are positioned behind each other on the same axis. Therefore, during a half period of an alternating field, a magnetic pole array generated by the coils is varied from S-N-N-S to N-S-S-N, S meaning south pole and N meaning north pole. Such a coil arrangement creates a multipole field with a dominant quadrupole component. Each coil contains 83 windings of copper wire wound on a core made of synthetic material. The differential coils are assembled by means of interconnecting plastic pieces to form a tetrahedron with an edge length of approximately 16 cm.
As sensor 6, a miniaturized induction coil may be used. Such a coil may consist of 1000 windings of insulated copper wire having a diameter of 20 μm wound on a piece of soft iron. By this, a sensor may be manufactured having outer dimensions of 8 mm×0.8 mm diameter. Preferably a coating is provided consisting of a thin film of synthetic material. The alternating magnetic field created by the field generator 2 induces an alternating voltage in the sensor, which is measured by the calculation unit connected to the sensor 6.
The coils of the field generator 2 are excited one after the other during a measurement cycle by an alternating current of ±2 A at 12 kHz for 3.3 ms each. Thus, one measurement cycle requires approximately 10 ms. During each cycle, the corresponding induction voltages determined by the sensor 6 are measured and evaluated by the calculation unit 4.
Using six induction voltages induced in the sensor by the six differential coils of the field generator 2, three Cartesian coordinates and two angles may be identified.
An algorithm to calculate the position of the sensor 6 within the space of the capture range may be taken from Seiler et al “A novel tracking technique for the continuous precise measurement of tumor positions in conformal radiotherapy”, Phys. Med. Biol. 45 (2002) N103-N110, which is hereby incorporated by reference. The calculation unit 4 may comprise a digital signal processor (DSP) and a digital to analog converter (DAC). Furthermore, the calculation unit 4 comprises a localizer system.
At the start of the method, the BOM or capture range 14 is large. In this capture range 14, the accuracy and resolution is low. At this stage shown in
The position and size of the capture range 16 is controlled such that it is centered around the region of interest a. Since the capture range 16 was more focused, measurements having a higher accuracy and better resolutions are possible: ra=r1±dr1 with dr1<dr0 (where dr0 and dr1 are uncertainties in position). Due to the capture range having a reduced size, a higher frame rate of acquisition is possible because the system has to track only one target, namely the region of interest at one time and not all three targets a, b and c at the same time. This centering of the capture range and reducing the size of the capture range can be iterated to provide an even higher accuracy and precision with a step wise smaller box of motion and capture range until the desired accuracy and resolution or the highest possible accuracy and resolution of the system are reached.
As shown in
If, after a refinement of the capture range or BOM with respect to one region of interest, another region of interest lies outside the BOM, such as region of interest b in
If it happens that a moving target escapes a box of motion and thus cannot be tracked any more, the system can be switched back to a larger box of motion. Having done this, the capture range is enlarged and thus the target can again be aimed at, centered to and tracked.
As can be taken from
The present invention may advantageously be applied in applications which are given by the localization, tracking and navigation in a catheter laboratory, where the navigation aids a physician in the placement of interventional devices such as catheters, balloons or stents. Also, advantageously, the present invention may be applied in coronary applications or during other procedures such as electro-physiology (EP). Advantageously, by applying the present invention, x-ray imaging of devices with virtual position information can be omitted, which allows to decrease an x-ray dose applied to the patient. However, the present invention may also be applied in other applications such as in fields of a targeted drug delivery in the context of molecular imaging where the local administration of medicine or drugs is a fundamental part of the process.
The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understandting the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
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|1||Gatehouse, P.D., et al.; Tracking local volume 3D-echo-planar coronary artery imaging; 2002; IEEE; abstract.|
|2||Seiler, P.G., et al.; A novel tracking technique for the continuous precise measurement of tumour positions in conformal radiotherapy; 2000; Phys. Med. Biol.; 45:N103-N110.|
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|U.S. Classification||324/207.15, 324/225|
|International Classification||A61B5/06, H01F5/00, G01B7/15, A61B6/12, G01N27/72|
|Cooperative Classification||A61B6/12, A61B6/469, A61B5/061, A61B5/06|
|European Classification||A61B5/06C, A61B6/46D4, A61B5/06|
|Jun 23, 2006||AS||Assignment|
Owner name: KONINKLIJKE PHILIPS ELECTRONICS N V, NETHERLANDS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BORGERT, JORN;RASCHE, VOLKER;REEL/FRAME:017831/0992
Effective date: 20040702
|Sep 22, 2011||FPAY||Fee payment|
Year of fee payment: 4
|Jan 8, 2016||FPAY||Fee payment|
Year of fee payment: 8